516 Life-histories of Northern Animals 



The sub-family Microtincs includes all our Short-tailed 

 Meadow-mice or Voles, the Lemmings, and the Muskrats. 

 All have the same dental formula : 



Inc. ^; mol. — = i6 



It comprises 7 genera. Their external characters as here 

 set forth will answer for a key: 



Microtus Schrank, 1798. The common Meadow- 

 mice or Voles in a coat of dark brown, with 

 pepper-and-salt effect on back, but paler and 

 grayer below; tail i^ to 2| times as long as 

 hind-foot. Molars not rooted, but from persist- 

 ent pulp. 



P/?^nflcom3?i- Merriam, 1889. Is like M/rrofwj-. When 

 adult it has molars with prong-like roots and 

 with reentrant angles deeper on inner than on 

 outer side; unfortunately these, though impor- 

 tant, are characters of little use to the field 

 naturalist. Hind-foot, 6-tuberculate, the outer 

 tubercle large and prominent, while in Microtus 

 it is nearly obsolete. 



Synaptomys Baird, 1857. Much like a Microtus, with 

 a very short tail, shorter than hind-foot, and with 

 upper incisors grooved on outer edge; in Microtus 

 they are smooth. 



Lemmus Link, 1795. Like a Microtus, with soft, 

 woolly fur, and very short tail, shorter than hind- 

 foot; the thumb has a flat strap-like nail', the 

 outer ear is well developed. 



Dicrostonyx Gloger, 184 1. Like Microtus, but with 

 tail a mere stub, much shorter than the hind- 

 foot. Outer ear rudimentary. The thumb ap- 

 parently wanting or a mere rudiment with a pm- 

 point nail; the two middle claws of the front 

 feet develop enormously and become two snow 



